1. Field Of The Invention
The present invention relates generally to vehicle wheel trim and more particularly to a welded metal trim ring and a blank from which it is formed, with the blank specifically configured to preclude stress failure during manufacture.
2. Description of Background Art
Trim rings have been employed on motor vehicle wheels for many years. Generally, such items comprised a decorative metal contoured outer ring and an inner grip annulus having teeth which engaged the wheel rim. Due to the highly corrosive environment of the typical environment, plated steel and other metals were unacceptable for high quality, OEM type applications; stainless steel has been specified.
Fabrication techniques employed heretofore have included, in the construction of the outer rings, the utilization of elongate rectangular sheet metal blanks which were joined at their ends to form endless cylindrical bands. The bands were thereafter cold formed, utilizing dies. Typical configurations specified up to a 25% enlargement in ring diameter with cold forming. Unfortunately the stresses generated during forming resulted in cracking or tearing of the metal band at the weakest points, which were the ends of the weld.
Although notching of the peripheral edges of the blank adjacent its ends with U-shaped cut outs was attempted the cut outs were generally ineffective with respect to preventing stress cracks and tears upon expansion of the band during subsequent forming.
Examples of dies and forming operations which represent attempts to avoid such stress failure were illustrated in U.S. Pat. No. 4,068,362, issued Jan. 17, 1978, and U.S. Pat. No. 4,084,526, issued Apr. 18, 1978. Both patents disclosed a technique of forming an outer ring from a welded metal cylindrical band by radial expansion at mid-width rather than at a peripheral edge of the band. By such technique, virtually no forming stresses were generated at the ends of the weld and the need for relieving stresses at such weak points was alleviated. Unfortunately, the dies were complicated, costly, and did not provide versatility in the available trim ring contours as compared with conventional forming dies. Further, additional manufacturing steps were required with respect to splitting a band at mid-width.
Another problem encountered in the manufacture of trim rings was that, at the beginning of each weld, the welding apparatus tended to burn through the thickness of the blank, creating weakness in the structure and a surface unsuitable for exposed decorative purposes. Further, although plasma type welding techniques have been utilized in forming stainless steel bands, the metallurgic structure of the blank adjacent the weld was often altered and physical characteristics different from that at the remainder of the band were possible. In some instances, the different physical characteristics were a function of the heat transfer parameters of the metal blank.
In order to reduce the tendency of burn through, copper tabs were proposed to be added to the peripheral edge of the metal blank at a location which was the beginning of the weld stroke. Of course, copper contamination of the blank was a possible risk concomitant with such approach and the proposed procedure resulted in added manufacturing costs in both labor and materials.